EFFECTS OF THE PROCESS CONDITIONS DURING DRY-DEFIBRATION ON THE PROPERTIES OF CELLULOSIC NETWORKS

The influence of structural changes caused by dry-defibration of the p ulp on the mechanical properties of dry-formed cellulosic networks has been investigated. The effects of fibre length, fibre curl and conten t of fine material on these properties are discussed. The fluff pulps used were one CTMP-grade and two kraft pulps. The primary parameters u sed to describe the networks were the storage modulus, G'(o) (measured at low strain amplitudes), and the critical strain, gamma(c) (at whic h the network yields), obtained from dynamic-mechanical measurements, and the maximum force, F-max, sustained by the network and the maximum strain, gamma(max) (at F-max), measured with a specially constructed shear tester. It was noted that the storage shear modulus, G'(o), and maximum force, F-max, were affected in the same manner by the defibrat ion conditions. To improve the deformability of the cellulosic network before rupturing, the ideal dry-defibration process should provide a greater number of free fibres per unit volume without producing fine m aterial, at the same time as the curl index of the fibres should incre ase. Long and curled fibres are thus to be preferred. (C) 1998 Chapman & Hall.